Multiscale Engineering of (Photo)electrocatalysts for Renewable Fuel Production

Abstract

Global warming is scientifically proven as a root of anomalous climate patterns such as ever-lasting drought, widespread flooding, continual sea level rise, or uncontrollable wildfire. These changes have devastating effects on human lives and any living species on our planet. This issue and an ever-growing demand for energy consumption are two of the grand challenges facing humankind now and coming decades. Scientific evidence has shown that the excess of the greenhouse gasses, primarily comprised of carbon dioxide (CO2), which traps the solar radiation inside the earth's atmosphere, resulting in a rise of the global temperature, is the primary source of these issues. Reducing the CO2 concentration in the atmosphere is thus a direct solution. In fact, most of the CO2 emission is originated from the combustion of the fossil fuels such as petroleum, natural gasses, or diesels in anthropogenic activities including transportation, agriculture, or industry. Therefore, reducing the CO2 concentration in the atmosphere by transforming it into other value-added fuels and using alternatively renewable energy sources, not producing CO2 during the fuel-to-power conversion must be imperatively addressed.

Thanks to the advances in science and technology, we now know ways to achieve our goals. By splitting water into hydrogen fuel, a dream of a clean power is closer than ever, and likewise scientists can now convert CO2 into valuable fuels such as formic acid, ethanol, ethylene, etc. The core technology in these processes lies on (photo)electrochemical conversion of water or CO2. In fact, electrolysis of water to hydrogen is an industrial process, heavily relying on rare-earth catalysts such as Pt-, Ru-, or Ir-based materials, while the CO2 reduction is still on a laboratory scale. For large-scale and practical utilization, catalysts must be not only highly active, earth-abundant, but also long-lasting. Therefore, during my Ph.D. I am going to develop low-cost, efficient, and stable catalysts for (photo)electrochemical conversion of water and CO2 into hydrogen and formate using an industry-relevant synthesis platform-flame spray pyrolysis (FSP).

We firstly present details of the literature regarding the feasibility, versatility, and scalability of FSP. Nanostructures of the most efficient BiVO4 photocatalyst is then fabricated via FSP for efficient photooxidation of water, and the impacts of BiVO4 structural properties on the photooxidation performance have been systematically investigated. The surface chemistry of a catalyst plays a vital role in dictating outcome performance; therefore, we study the role of vanadium vacancies in BiVO4 photoanodes for photooxidation of water in the next work. It is a formidable challenge to have excellent light absorption and fast reaction kinetics for efficient PEC process, simultaneously. Hence, co-catalysts are often incorporated with photocatalysts to boost the reaction kinetics. Multi-scale engineering of cobalt oxide electrocatalyst for high OER activity and stability is thus studied. In this work, we provide insights into the interplay between activity and stability of Co3O4 electrodes for oxygen evolution reaction (OER). Likewise, to reduce the atmospheric CO2 concentration conversion of CO2 into value-added productions to close the carbon cycle must also be successfully attained. As such, nanostructured Bi2O3 fractals for highly selective CO2 electroreduction to formate are synthesized, characterized and tested in comparison with non-fractal counterparts. The performance of this novel fractal structure of the Bi2O3 can be further improved to reach the maximum faradaic efficiency toward formate by being intercalated with Au nanoparticles to generate uniformed nanostructures of Au-Bi2O3 fractals. Finally, a summary of the results in this thesis and a short outlook into the future studies will be presented. Show more